WASHINGTON (CNN) --White House hopeful Bob Graham sent a letter to President Bush on Monday, asking him to release censored parts of a critical congressional report on U.S. intelligence on terrorism and the attacks of September 11, 2001.

Graham, who has emerged as a particularly outspoken critic of the Bush administration on its handling of intelligence matters, hints broadly that the classified sections have to do with Saudi Arabia and terrorism. He does not explicitly say so, but in the letter he quotes from Saudi Arabia's ambassador to the United States, who has strongly criticized reports that his country has supported terrorists.

Declassifying more intelligence information, Graham wrote, could clear up the matter.

"That will permit the Saudi government to deal with any questions which may be raised in the currently censored pages, and allow the American people to make their own judgment about who are our true friends and allies in the war on terrorism," wrote Graham, a former chairman of the Senate Intelligence Committee.

The censored passages deal with information that suggest "specific sources of foreign support for some of the Sept. 11 hijackers while they were in the United States," according to a summary in the congressional report. Fifteen of the 19 hijackers were Saudi nationals.

The Florida Democrat has been among Bush's harshest critics of late. Over the weekend, Graham repeated his criticism that Bush "knowingly" misled the American people about the reasons for going to war in Iraq and said that was an impeachable offense.

"Clearly, if the standard is now what the House of Representatives did in the impeachment of Bill Clinton, the actions of this president [are] much more serious in terms of dereliction of duty," the Florida Democrat said on Fox News Sunday.

Other Democrats have said they don't agree with Graham's characterization, even if they do have questions about how the White House handled intelligence information both before the September 11 attacks and in the buildup to the war with Iraq -- which Bush has cast as part of the broader war on terrorism.

Graham is not alone is his call for the release of more information from the congressional report on September 11.

Some Republicans say they want the same thing.

For example, Sen. Richard Shelby, R-Alabama, who was ranking Republican on the Senate Intelligence Committee during the joint congressional probe into the tragedy, said that in his judgment, "95 percent of that information could be declassified."

"I think [the pages] are classified for the wrong reason," he said Sunday on NBC's Meet The Press, adding that the pages were being withheld because the information "might be embarrassing to some international relations."

Current Senate Intelligence Committee Chairman Pat Roberts, R-Kansas, told CBS's Face The Nation he was "unhappy with the amount of material that was redacted." He also said that at least part of the congressional report was redacted to "protect the Saudis," adding that "there was obvious Saudi involvement" in the hijackings.

The Saudi government has refuted that charge, calling it "malicious and blatantly false."

In a statement released last week, Prince Bandar bin Sultan, the Saudi ambassador to the United States, suggests his country would like the 28 blanked-out pages to be released.

"Saudi Arabia has nothing to hide," said in the statement. "We can deal with questions in public, but we cannot respond to blank pages."